Rod Drop - Allen-Bradley 1444-TSCX02-02RB User Manual

Chapter 4 Measurement Definition
170
Download the new configuration and observe the measured value.
Make sure that it displays the correct temperature.
The preceding example shows that the measured output from the
accelerometer temperature channel was 230.9 mV or 23.1 °C. So the observed
value, 23.2504, is correct.

Rod Drop

Used in reciprocating compressors, Rod Drop is a measure of the position of
the piston rod relative to the proximity probe mounting location. Rod Drop
provides an indirect measurement of wear of the piston rider band.
Because the distance between the probe and the piston rod varies over the
length of the stroke of the rod, the measurement must be triggered such that it
is performed consistently at the same point in the stroke. To accommodate this
feature, when you configure a Rod Drop measurement, the tachometer trigger
signal is used to trigger when the measurements are taken on each piston rod
(channel).
The relationship between the position of each reciprocating piston rod and the
rotating trigger position (tachometer trigger) is a function of the specific
mechanical design of the machine. Therefore, before defining the Rod Drop
measurements, determine, for each piston:
• What the mechanical relationship is between the tachometer trigger
point and the position of the rod in its stroke.
• Where to take the measurement along the piston rod. The Rod Drop
measurement is the average of the samples that are taken between the
Start and Stop positions, as defined by the Trigger Angle and the
Angular Range.
• The minimum speed for rod drop measurements is 10 rpm. Below 10
rpm the measurement defaults to a normal DC measurement.
• The maximum speed for rod drop measurements is calculated and based
on sample rate and the selected Angular Range:
Maximum rpm = (2929 * Angular Range) / 6
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018